Numerous measures to influence the filling process of mold cavities have previously been described in the prior art. Each type of melt has certain suitable gate velocities and gating systems. Since a maximal gate velocity must not be exceeded, it is necessary for the cross-section of the gate surface and thus for the part of the gating system that allows for separation of the sprue part from the die casting mold after the casting process to have sufficiently large dimensions. With extensive and thin-walled cast parts, this requirement leads to a great proportion of circulating material, the mass of which can lie in the range of the mass of the cast part itself. The circulating material is subsequently melted again, which requires a considerable supply of external energy.
In order to reduce the amount of circulating material, DE 10 2011 050 149 A1 describes arranging a casting valve in form of a pressure casting die directly on the gate area of the die casting mold. The casting valve is at first kept open by a resistance heating. Turning off the heating leads to the formation of a plug and thus to a closing of the casting valve. A controlled or temperature-independent closing of the valve is not possible. In order to be opened, the plug must be reliably melted, which lengthens the duration of the process and requires an overall higher energy supply per cast part due to temperature fluctuations.
Another, controllable, casting valve for metal melts is described in DE 34 27 940 A1. The melt portion is inductively supplied in a dosed manner by the casting valve and a shutoff occurs in conjunction with spatial limitation elements.
DE 10 2007 047 545 A1 describes a casting valve that is closable by means of a piston. The piston is axially displaceable in a valve housing. In order for concentricity errors of the piston to not lead to inhomogeneous melt streams and to provide a reliable closing of the casting valve, the piston-skirt surface forms a greater angle relative to the main axis of the valve than the valve housing in the run-out area. The piston forms an annular contact surface with the housing wall in the closed state.
The two latter casting valves can be used for reliable filling of a mold cavity with a predetermined melt portion. However, in order to compensate for material shrinkage during the solidification of the cast part, it is necessary to continue to supply melt. To this end, the previously mentioned casting valves can remain open until the shrinking process has ended which requires heating at least until it is closed and complicates an exact dosage. A second mechanism is alternatively required which fills the hollow space formed because of the shrinking process by post-feeding and post-compressing melt. The casting valve and the post-compression mechanism must be synchronized. This is, however, complicated, leads to an extensive build of the casting device, and thus increases the amount of energy required for heating.